Saturday, June 1, 2013

NASA's Actual Plan to Deflect an Approaching Asteroid

Asteroid

Asteroids are frightening things. With the approach of QE2, a big one that would end civilization, the galaxy briefly put Earth on notice.

Thankfully, QE2 is slated to miss the planet tonight.

"Scientists have concluded that the asteroid poses no threat to planet Earth," White House spokesman Josh Earnest told reporters on Friday, reassuring mankind it will live another day. "I never really thought I'd be standing up here saying that, but I guess I am."

But what if an asteroid were headed straight for Earth?

NASA evidently has us covered. In 2005, in a bill authorizing space-program funds, Congress asked NASA for a plan to identify, track and deflect - yes, deflect - all manner of PHOs (potentially harmful objects) that could pose a threat.

The directive, according to NASA, is known as the George E. Brown Jr. Near-Earth Object Survey Act, named after the late Democratic chairman of the Committee on Science, Space and Technology, who died in 1999 and didn't live to see NASA's asteroid plan on paper. Rep. Dana Rohrabacher, R-Calif., successfully included it in the 2005 bill.

With that congressional prompt, NASA considered many science-reality options, including some that bore resemblance to film plots.

Among the solutions NASA studied were firing a nuclear missile at the asteroid, landing a nuclear bomb on the surface, drilling into the great space rock and exploding a nuclear bomb there (which Bruce Willis attempted to do in the film, "Armageddon"), and all those same strategies with conventional bombs.

The scientists also gamed out some weirder possibilities designed with more warning time in mind.

Those included flying a spacecraft near the asteroid for a long time to act as a "gravity tractor" and pull it off course (deemed ineffective, unsurprisingly); using a large mirror to focus sunlight and "boil off" some material from the asteroid; a spacecraft "rendezvous" with the asteroid to "boil off" some material using a "pulse laser"; landing on the asteroid, drilling into it, and "eject[ing] material from PHO at high velocity"; "attach[ing]" a spacecraft to the asteroid and pushing it out of the way; and what NASA called the "Enhanced Yarkovsky Effect" - altering the reflectiveness of a rotating asteroid and counting on the "radiation from sunheated material" to push the asteroid off course.

NASA charted how effectively each method could push a gigantic space rock off course.

The blue horizontal lines show different scenarios and the momentum change needed to deflect them. The top line (F) shows the amount of momentum change needed to deflect a comet with short (nine to 24 months) warning. The bottom lines, A1 and A2, show two scenarios for "[t]he 330 meter asteroid, Apophis, before its close approach to Earth in 2029."

NASA Chart 1NASA chart 2

The winner: nuclear bomb. For a fast-approaching comet, the only recourse may be drilling into it and detonating a nuclear bomb, as the top line in the top graph shows.

But, in general, NASA favored simply firing a missile at a space rock and detonating it nearby. Landing on the asteroid, or drilling into it, would make for a better explosion, but NASA was wary of fragmenting the big rock.

Unfortunately, nuclear explosions in space are banned under a 1 967 U.N. space treaty, so other nations would have to sign off on the plan.

From the 2007 NASA report to Congress:

In the impulsive category, the use of a nuclear device was found to be the most effective means to deflect a PHO. Because of the large amount of energy delivered, nuclear devices would require the least amount of detailed information about the threatening object, reducing the need for detailed characterization. While detonation of a nuclear device on or below the surface of a threatening object was found to be 10-100 times more efficient than detonating a nuclear device above the surface, the standoff detonation would be less likely to fragment the target. A nuclear standoff mission could be designed knowing only the orbit and approximate mass of the threat, and missions could be carried out incrementally to reach the required amount of deflection. Additional information about the object's mass and physical properties would perhaps increase the effectiveness, but likely would not be required to accomplish the goal. It should be noted that because of restrictions found in Article IV of the "Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space," including the Moon and Other Celestial Bodies, use of a nuclear device would likely require prior international coordination. The study team also examined conventional explosives, but found they were ineffective against most threats.

So there you have it: The government's plan if an asteroid approaches is to shoot a nuclear missile at it. The planet has George E. Brown, Dana Rohrabacher and NASA to thank.